1. Field of the Invention
The present invention relates to electron beam apparatus capable of high-resolution observation at low acceleration voltages.
2. Description of the Related Art
In recent years, semiconductor integrated circuit patterns are shrinking more and more, which in turn strongly requires, during semiconductor microfabrication processes, an enhanced ability to achieve SEM observation thereof with higher resolution at low acceleration sample incidence voltages of 1 kV or less. To this end, it is important to reduce aberration of an objective lens of a SEM mirror tube or barrelxe2x80x94especially, chromatic aberration. Methods for doing this include a method for employing in combination a composite objective lens with a single-pole or xe2x80x9cmonopolexe2x80x9d magnetic field type lens and an electrostatic lens. As shown in Japanese Patent Laid-Open Nos. 199459/1998 and 25895/1999 (FIGS. 4 and 5), electrodes 3a, 43b (xe2x80x9c3xe2x80x9d in FIG. 5) are provided between a monopole lens 4 and sample 5 for applying the same voltage potential of negative polarity to the electrode 43b (3 in FIG. 5) and the sample 5 to thereby reduce aberration of an objective lens while at the same time suppressing astigmatic aberration or astigmatism otherwise occurring due to sample tilting thereby enabling accomplishment of high-resolution observation. However, since it is of the structure with a built-in electrostatic lens mounted between a single magnetic pole and sample, the resulting distance between the single magnetic pole""s top surface and the sample becomes relatively larger; thus, it has been difficult to further reduce the aberration.
Other prior known examples of the composite lens using a combination of the monopole lens and electrostatic lens with the sample-opposing electrode made of magnetic material are as follows.
In an example disclosed in Japanese Patent Laid-Open No. 17369/1998 (FIG. 6), xe2x80x9cmagnetic poles (8, 8a) of an objective lens have a shape for creating a magnetic field on the sample side while comprising one or more axially symmetrical acceleration electrodes (10a, 10b) disposed in an axial direction of an electron beam passage unit of the objective lens for enabling penetration of primary electrons, means for applying a positive voltage to the acceleration electrodes, an electric field correction electrode (11) capable of permitting penetration of the primary electrons, which is disposed outside of a specified electrode (10b) of said acceleration electrodes that is nearest to the sample or alternatively disposed on the sample side, and means for applying a negative voltage to the correction electrode, wherein . . . the electrode (10b) of said acceleration electrodes nearest to the sample is comprised of a magnetic material . . . . xe2x80x9d However, in view of the fact that the electrode 10b made of magnetic material is applied a positive voltage potential and the sample is set at Earth potential, once the sample is tilted, the electric field near or around an optical axis becomes asymmetrical resulting in a decrease in secondary electron detection efficiency along with creation of aberration. It is the one that attempts to solve this problem by canceling or bucking by an electric field of the electric field correction electrode 11 as provided outside of the electrode 10b; obviously, this must cause an application voltage to the electrode to change depending upon a tilt angle of the sample, resulting in an increase in troublesome procedure while increasing complexities of arrangement.
In another example disclosed in Japanese Patent Laid-Open No. 120950/1999 (FIG. 7), a third pole piece (13) is installed between a first pole piece (70) and a second pole piece (71) in a similar way to that of the above-noted example, wherein xe2x80x9cthe third pole piece . . . is not magnetically contact with the other two pole pieces and is put in . . . a magnetic field . . . as formed between the first and second pole pieces for extraction of part of this magnetic field,xe2x80x9d thereby enabling application of a positive or negative voltage potential to the third pole piece. However, in case a negative voltage potential is applied to the third pole piece, since the sample is applied no voltage potentials, there inevitably occur when tilting the sample a decrease in secondary electron detection efficiency and creation of aberration as in the above-stated related art.
An object of the present invention is to achieve further improved resolution in low-acceleration voltage electron beam apparatus, especially while tilting a sample.
To attain the foregoing object, in an electron beam apparatus in accordance with the invention as disclosed herein,
Firstly, a sample is installed within a lens magnetic field as formed adjacent to a magnetic pole placed on the side of an electron source, wherein the electron source-side magnetic pole is subdivided into a magnetic pole spaced far from the sample and a magnetic pole near the sample, and wherein an electromagnetic field composite lens is provided for applying negative voltage potentials to the magnetic pole (3b) near the sample and the sample when the sample is tilted.
Second, the magnetic pole near the sample and the sample are arranged so that these are applied the same voltage potential of the negative polarity.
Third, a top surface of the magnetic pole (4a) far from the sample is placed closer in position to the sample than an electrically insulative material between the magnetic pole far from the sample and the magnetic pole near the sample.
Fourth, the magnetic pole near the sample and the sample are applied the same voltage potential of the negative polarity.
Fifth, a sample is installed between mutually opposing magnetic poles, that is, a magnetic pole placed on the side of an electron source and a magnetic pole placed on the opposite side to the electron source, wherein the electron source-side magnetic pole is further subdivided into a magnetic pole far from the sample and a magnetic pole near the sample, and wherein an electromagnetic field composite lens is provided for applying negative voltage potentials to the magnetic pole (3b) near the sample and the sample when the sample is tilted.
Sixth, the sample and the magnetic pole opposing this sample are applied the same negative voltage.
Seventh, a top surface (4a) of the magnetic pole far from the sample is placed closer to the sample than an electrical insulative material between the magnetic pole far from the sample and the magnetic pole near the sample.
Eighth, the near-the-sample magnetic pole and the sample are applied the same voltage potential of the negative polarity.
Ninth, a sample is installed between opposing magnetic poles, i.e. a magnetic pole placed on the side of an electron source and a magnetic pole placed on the opposite side to the electron source, wherein the electron source-side magnetic pole is further subdivided into a magnetic pole (4a) far from the sample and a magnetic pole (3b) near the sample, wherein the magnetic pole on the opposite side to the electron source is further divided into a magnetic pole (3bxe2x80x2) near the sample and a magnetic pole (4axe2x80x2) far from the sample, and wherein an electromagnetic field composite lens is provided for applying negative voltage potentials to the both magnetic poles (3b, 3bxe2x80x2) near the sample and the sample (5) when the sample is tilted.
Tenth, the same voltage potential of negative polarity is applied to the sample and the both magnetic poles which oppose the sample.
Eleventh, at a respective one of the electron source-side magnetic pole and the magnetic pole on the opposite side to the electron source, a top surface of the magnetic pole (4a, 4axe2x80x2) far from the sample is placed nearer to the sample than an electrical insulative material (7, 7xe2x80x2) between the magnetic pole far from the sample and the magnetic pole near the sample.
Twelfth, the same voltage potential of negative polarity is applied to the magnetic pole near the sample and the sample.
Thirteenth, it is possible, when the sample is not tilted, to apply the voltage potential of the magnetic pole near the sample on the electron source side at a zero or positive voltage potential.